1. Field of the Invention
The present invention relates to a method for feeding concrete or other thick materials from a container into a feeding pipe by means of two feeding cylinders which are alternately connectable by a switching device to the container or the feeding pipe, with the feeding pistons of the feeding cylinders alternately performing a suction stroke and a pressure stroke, and the average piston speed during the suction stroke being at least temporarily greater than during the pressure stroke, and to an apparatus for performing the method.
2. Description of the Related Art
A corresponding method and a corresponding apparatus are known from German patent specification 3525003. The gist of the known method consists in the feature that the first feeding cylinder has not yet finished its pressure stroke, while the second feeding cylinder already starts with its pressure stroke at a lower feeding speed. After the first feeding cylinder has finished its pressure stroke, the switching operation of the switching device is started, while the second feeding cylinder continues its feeding operation at a lower feeding speed. Such a procedure has the effect that the concrete in the second feeding cylinder is already advanced, so that after the switching operation of the switching device the concrete column in the feeding pipe has no chance to perform an excessive rebound movement. This method, and the apparatus used therefor, have proved to be successful in general. However, in the present technical field, demands for more and more efficient methods for concrete feeding machines have been made recently. For instance, serious attempts have been made to increase the length of the feeding pipe and thus, in particular, the feeding height. Since in the known method the pumping operation is carried out at a reduced feeding speed during the switching period, a small pulsation is created in the feeding flow. Such a pulsation could be disregarded under the feeding conditions which have so far prevailed, but will lead at the feeding heights that are now demanded, and thus at the great lengths, for instance in the case of an arm of a concrete conveying vehicle, to vibrations at the feeding pipe end.